The present invention relates to the reaction, known as hydrosilation, in which a silane or polysiloxane which is substituted with hydrogen and with halogen, alkyl and/or alkoxy groups is reacted with an olefin. This invention is directed in particular to hydrosilation of silanes, but can include also other species as discussed below.
The reaction of hydrosilatable olefins, such as allyl chloride or 1-octene, with hydrosilanes such as trimethoxysilane, in the presence of an appropriate catalyst, is known. An example is disclosed in U.S. Pat. No. 5,559,264, which is directed to the reaction of allylic chloride with hydromethoxysilane in the presence of ruthenium catalyst. A continuous hydrosilation process with recycle is disclosed in German Offen. 196-32157 Al, wherein conversion of the limiting reactant is limited to less than 80% to minimize a side reaction inherent to hydrosilation reactions between chlorosilanes and allyl chloride. Limiting conversion to less than 80% is a disadvantage for hydrosilation reactions not afflicted with significant side reactions.
There is interest in finding improved modes of carrying out the hydrosilation reaction. Improvements are elusive because of the variety of byproducts that typically are formed, their properties, and the need to control their formation and to remove those that do form from the desired silane product. In addition, the hydrosilation reaction itself is sensitive to a number of conditions such that it can become necessary to balance competing effects and to accept non-optimum results.
Certain process schemes for carrying out the hydrosilation reaction, while effective, pose drawbacks. For instance, typical batchwise operation produces a crude product containing the desired hydrosilated silane product in mixture with byproducts and one or more unreacted reactants. This crude product needs to be treated to recover the desired product in a subsequent stage, and it needs to be stored until it is passed to that stage. This storage, even temporary, poses a risk of degrading of the product, as well as a risk of the crude product undergoing cross-reaction with potentially hazardous and even explosive effect. Also, storing crude product within the reaction scheme represents an accumulated inventory of material which raises the overall cost of the process. If the crude product contains substantial amounts of unreacted silane, safety considerations may dictate more costly equipment for handling or storage.